Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-12-19
2003-11-25
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
Reexamination Certificate
active
06654580
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus in which an electrophotographic technique and the like are utilized to transfer image information onto a transfer material and to form an image, particularly to driving connection of the image forming apparatus.
DESCRIPTION OF RELATED ART
In a conventional image forming apparatus in which an electrophotographic technique has heretofore been employed, an electrophotographic photoconductor served as an image carrier is charged by a charging unit, and irradiated with light corresponding to the image information, to form a latent image thereon. A toner image formed by developing the latent image by a developing unit is transferred to a sheet material and the like so that the image is formed.
In such an image forming apparatus, there is a technical problem as to minimizing an image jitter, density unevenness and transfer position deviation. Examples of factors which determines such properties include a speed fluctuation of the photoconductor, and it is very important to develop a driving unit having little speed fluctuation.
A driving system of a conventional image forming apparatus will be described hereinafter with reference to
FIGS. 26 and 27
.
FIG. 26
is a perspective view showing a driving unit and a photoconductor drum of the conventional image forming apparatus, and
FIG. 27
is an explanatory view showing an engagement state of a driving spline and a follower spline of FIG.
26
.
In
FIG. 26
, a driving unit
2
has involute spline shafts (driving splines)
18
for transmitting a rotation force to photoconductor drums (photoconductors)
1
a
to
1
d
as image carriers. The involute spline shaft
18
is rotated by a driving motor (not shown) via a reduction mechanism (not shown). The rotation force of the spline shaft is transmitted to each of involute spline holes (follower spline)
19
mounted on rotation shafts of the photoconductor drums
1
a
to
1
d
, so that the photoconductor drums
1
a
to
1
d
are rotated.
However, there is looseness in the spline engagement between the involute spline shaft
18
and the involute spline hole
19
. Particularly, with respect to the looseness of a peripheral direction, the photoconductor drums
1
a
to
1
d
are moved by the looseness when a load fluctuates. This generates an image jitter, density unevenness, and transfer position deviation.
In actual, various mechanisms are necessary for forming the images in peripheries of the photoconductor drums
1
a
to
1
d
. Examples of such the mechanisms include developing means (not shown) for developing electrostatic latent images formed on the photoconductor drums
1
a
to
1
d
, transfer means (not shown) for transferring the toner images developed on the photoconductor drums
1
a
to
1
d
to a transfer material, and the like. Rotations of the photoconductor drums
1
a
to
1
d
are influenced by rotation and load fluctuations of these mechanisms, and the drums are easily moved.
To solve the problem, as shown in
FIG. 26
, torque limitters
21
a
,
21
b
,
21
c
,
21
d
are attached as load means to the photoconductor drums
1
a
to
1
d
. The looseness of the peripheral direction in the spline engagement between the involute spline shaft
18
and the involute spline hole
19
is constantly removed in one direction, that is, a rotation direction P as shown in
FIG. 27
, so that the photoconductor drums
1
a
to
1
d
steadily rotate.
However, of the photoconductor drum requires the load means such as the torque limitters
21
a
,
21
b
,
21
c
,
21
d
for constantly displacing the engagement looseness in the peripheral direction of the spline in one direction. Therefore, in the aforementioned conventional driving technique, there is a first problem that a driving force increases, the driving unit is enlarged, and cost-up is caused.
Particularly, in a multi-image forming apparatus of a tandem system including a plurality of photoconductor drums, and the like, since the number of load means corresponding to the number of photoconductor drums are necessary, the driving force largely increases, and the problem becomes very large.
Moreover, the influence of the engagement looseness in the peripheral direction is reduced or canceled by the load means such as the torque limitter, but the looseness in a radius direction remains. Due to the looseness, rotation centers of the follower spline and a driving spline deviate, the rotation of the driving spline is not exactly transmitted to the follower spline, and the rotation fluctuation of the photoconductor drum is caused. Thus, there is a second problem that the image jitter, density unevenness, and transfer position deviation are generated.
Particularly, in the multi-image forming apparatus of the tandem system including the plurality of photoconductor drums, since the transfer position deviation results in color deviation, the problem becomes very serious.
Moreover, for color images, a large number of image forming apparatuses of the tandem system have heretofore been proposed in which a plurality of image carriers with the aforementioned series of image forming process developed therein is included, and respective color images such as cyan, magenta, and yellow images, and preferably a black image are formed on the respective image carriers, and are superposed and transferred onto a sheet material in transfer positions of the respective image carriers, to form a full-color image. The multi-image forming apparatus of the tandem system is said to be advantageous for a high speed because respective image forming sections are disposed for the respective colors.
For example, as described in specifications proposed by the present applicant and filed as JP-A-2000-284592, the multi-image forming apparatus of the tandem system includes: image forming units for forming toner images of respective colors such as yellow (Y), magenta (M), cyan (C), and black (K); an exposure unit for outputting an image signal and forming an electrostatic latent image; an intermediate transfer belt formed and run in a closed loop shape; and a fixing unit. The toner images on the intermediate transfer belt are transferred onto the sheet material supplied from a sheet cassette and fixed onto the sheet material by the fixing unit.
Since the respective image forming units of yellow (Y), magenta (M), cyan (C), and black (K) have a common structure, one of the image forming units is shown in FIG.
28
.
As shown in
FIG. 28
, the image forming unit is a combination of: a photoconductor unit including a photoconductor drum
102
having a peripheral surface with an electrostatic latent image formed thereon by a laser beam
109
d
of an exposure unit
106
d
, charging means
134
for charging the photoconductor drum
102
, and cleaning means
126
for removing a residual toner from the surface of the photoconductor drum
102
; and a developing unit including a toner supply roller
122
for supplying toner to a developing roller
121
which contacts the photoconductor drum
102
, and a layer thinning blade
123
, disposed in contact with the developing roller
121
, for uniformly thinning a toner layer and charging the toner layer at a predetermined potential.
In the image forming unit, the electrostatic latent image of image information is formed on the photoconductor drum
102
by the exposure unit
106
d
. The electrostatic latent image is visualized as the toner image by the developing roller
121
, and transferred onto the intermediate transfer belt. Moreover, in the four-colors image forming apparatus, the respective color toner images are transferred onto the intermediate transfer belt and the multi-color image is finally formed.
A conventional technique will be described hereinafter with reference to the drawings.
FIGS. 29
to
33
are perspective views showing a part of the conventional image forming apparatus in detail.
As shown in
FIG. 29
, for driving transmission of the photoconductor drum
102
in the conventional image forming apparatus, a gear driving system is used in many case
Kawano Yuzo
Shimada Masaya
Tajima Kazuhiko
Yamaguchi Naoki
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